I'm going to have to look at hysteresis more closely. I need to keep the ACS120 from turning on and off too quickly; the data sheet says that if it switches slower than once a second that a heat sink shouldn't be necessary. (I did put a small copper fin on it anyway.) I don't expect rapid temperature swings but I want to figure out what the delta for the thermistor is around 40F or so then do the math for a resistor value that'll give me a couple of degrees there.
It was late when I hit the "post" button and I sure did mean to mention that the unit is subject to noise and I do see it switch when it's in the hysteresis region and I turn some things on. There is a .1uF cap (forgotten in the schematic) across power to the opamp but I don't know how inputs are filtered; are you saying caps directly on plus and minus pins to their respective rails? I can do that...
Thank you, - Ed. [ Parent ]
(I didn't look up the op-amp data sheet: if it's CMOS you have to be careful to avoid causing SCR latchup in some circumstances, eg if the supply rails dip quickly leaving the capacitors to discharge though the op-amp input protection diodes. You could counter that in various ways but I think that unless you get to many uF you'll probably be fine in practice.)
Rgds
Damon[ Parent ]
